Isotopic assessment of sources and processes affecting sulfate and nitrate in surface water and groundwater of Luxembourg

Surface water and deep and shallow groundwater samples were taken from selected parts of the Grand-Duchy of Luxembourg to determine the isotopic composition of nitrate and sulfate, in order to identify sources and/or processes affecting these solutes. Deep groundwater had sulfate concentrations between 20 and 40 mg/L, delta34S(sulfate) values between -3.0 and -20.0 per thousand, and delta18O(sulfate) values between +1.5 and +5.0 per thousand; nitrate was characterized by concentrations varying between < 0.5 and 10 mg/L, delta15N(nitrate) values of approximately -0.5 per thousand, and delta18O(nitrate) values approximately +3.0 per thousand. In the shallow groundwater, sulfate concentrations ranged from 25 to 30 mg/L, delta34S(sulfate) values from -20.0 to +4.5 per thousand, and delta18O(sulfate) values from approximately +0.5 to +4.5 per thousand; nitrate concentrations varied between approximately 10 and 75 mg/L, delta15N(nitrate) values between +2.5 and +10.0 per thousand, and delta18O(nitrate) values between +1.0 and +3.0 per thousand. In surface water, sulfate concentrations ranged from 10 to 210 mg/L, delta34S(sulfate) values varied between -9.3 and +10.9 per thousand, and delta18O(sulfate) values between +3.0 and +10.7 per thousand were observed. Nitrate concentrations ranged from 10 to 40 mg/L, delta15N(nitrate) values from +6.5 to +12.0 per thousand, and delta18O(nitrate) values from -0.4 to +4.0 per thousand. Based on these data, three sulfate sources were identified controlling the riverine sulfate load. These are soil sulfate, dissolution of evaporites, and oxidation of reduced S minerals in the bedrock. Both groundwater types were predominantly influenced by sulfate from the two latter lithogenic S sources. The deep groundwater and a couple shallow groundwater samples had nitrate derived mainly from soil nitrification. All other sampling sites were influenced by nitrate originating from sewage and/or manure. A decrease in nitrate concentration observed along one of the rivers was attributed to denitrification. It appears that sulfate within Luxembourg's aquatic ecosystem is mainly of lithogenic origin, whereas nitrate is often derived from anthropogenic activities.     

Evaluation of the Sulfate Dynamics in Groundwater by Means of Environmental Isotopes

Abstract

Elevated sulfate concentrations and their heterogeneous distribution in the drinking water catchment area Torgau-Mockritz (Germany) were investigated by means of multiple isotope signatures such as δ³⁴S, δ¹⁸O-H₂O, δD, tritium, and ⁸⁵Kr. δ³⁴S values of the groundwater sulfate vary between -19…+ 37‰ CDT. No simple correlation exists between sulfate concentrations and δ³⁴S. Superimposition of different sulfur sources and mobilization processes combined with a complicated groundwater movement create a complex distribution pattern. The oxidation of reduced sedimentary sulfur has to be regarded as a main source of dissolved sulfate at least regionally. Tritium and ¹⁴C data revealed that old groundwater can be excluded as source for high sulfate contents. Correlated temporal variations in the concentrations of tritium and sulfate are observed in deeper sampling positions. Highly variable δ¹⁸O and δD, as detected in parts of the catchment area, indicate local influences of surface water infiltration into the aquifer. The spatial distribution of isotope signatures enables the identification of zones with descending younger water or hindered groundwater movement and hence provides useful hints for flow modeling.     

Seasonal variation of oxygen-18 in precipitation and surface water of the Poyang Lake Basin,China

Based on the monthly δ¹⁸O value measured over a hydrology period in precipitation, runoff of five tributaries and the main lake of the Poyang Lake Basin, combined with hydrological and meteorological data, the characteristics of δ¹⁸O in precipitation (δ¹⁸O_PPT) and runoff (δ¹⁸O_SUR) are discussed. The δ¹⁸O_PPT and δ¹⁸O_SUR values range from?2.75 to?14.12 ‰ (annual mean value=?7.13 ‰ ) and from?2.30 to?8.56 ‰, respectively. The seasonal variation of δ¹⁸O_PPT is controlled by the air mass circulation in this region, which is dominated by the Asian summer monsoon and the Siberian High during winter. The correlation between the wet seasonal averages of δ¹⁸O_SUR in runoff of the rivers and δ¹⁸O_PPT of precipitation at the corresponding stations shows that in the Poyang Lake catchment area the river water consists of 23% direct runoff (precipitation) and 77% base flow (shallow groundwater). This high proportion of groundwater in the river runoff points to the prevalence of wetland conditions in the Poyang Lake catchment during rainy season. Considering the oxygen isotopic composition of the main body of Poyang Lake, no isotopic enrichment relative to river inflow was found during the rainy season with maximum expansion of the lake. Thus, evaporation causing isotopic enrichment is a minor component of the lake water balance in the rainy period. During dry season, a slight isotopic enrichment has been observed, which suggests a certain evaporative loss of lake water in that period.     

Stable isotopic and geochemical variability within shallow groundwater beneath a hardwood hammock and surface water in an adjoining slough (Everglades National Park,Florida, USA)

Data from a 10-month monitoring study during 2007 in the Everglades ecosystem provide insight into the variation of δ¹⁸O, δD, and ion chemistry in surface water and shallow groundwater. Surface waters are sensitive to dilution from rainfall and input from external sources. Shallow groundwater, on the other hand, remains geochemically stable during the year. Surface water input from canals derived from draining agricultural areas to the north and east of the Everglades is evident in the ion data. δ¹⁸O and δD values in shallow groundwater remain near the mean of?2.4 and?12 ‰, respectively. ¹⁸O and D values are enriched in surface water compared with shallow groundwater and fluctuate in sync with those measured in rainfall. The local meteoric water line (LMWL) for precipitation is in close agreement with the global meteoric water line; however, the local evaporation line (LEL) for surface water and shallow groundwater is δ D=5.6 δ¹⁸O+1.5, a sign that these waters have experienced evaporation. The intercept of the LMWL and LEL indicates that the primary recharge to the Everglades is tropical cyclones or fronts. δ deuterium to δ¹⁸O excess (D_ex values) generally reveal two moisture sources for precipitation, a maritime source during the fall and winter (D _ex>10 ‰) and a continental-influenced source (D _ex<10 ‰) in the spring and summer.     

Pleistocene age paleo-groundwater inferred from water-stable isotope values in the central part of the Baltic Artesian Basin

A new data set of δ²H and δ¹⁸O in the groundwater from the central part of the Baltic Artesian Basin is presented. The hydrogeological section is subdivided into stagnation, slow exchange and active exchange zones. Na–Ca–Cl brine found at the deepest part – the stagnation zone – is characterized by δ¹⁸O values above ?5?‰ and δ²H values approaching ?40?‰ with respect to Vienna Standard Mean Ocean Water. The slow exchange zone where waters of mostly intermediate salinity reside is characterized by δ¹⁸O values around ?11.7?‰ and δ²H values around ?85.3?‰. Mean δ¹⁸O and δ²H values of the fresh groundwater in the active water exchange zone are ?11.1 and ?79.9?‰, respectively. Characteristically, the groundwater in the active and slow exchange zone is isotopically more depleted compared with the precipitation values observed, and the depletion increases with depth down to the level where strongly enriched brines are encountered.     

Regime Shift Signatures from Stable Oxygen Isotopic Records of Otoliths of Atlantic Cod (Gadus morhua)

Abstract

The sudden collapse of Atlantic cod (Gadus morhua) may relate to ocean climate, or regime shifts as demonstrated in production of Pacific salmon. This paper reports the results of stable oxygen isotope ratio analyses (¹⁸O/¹⁶O or δ¹⁸O_A) from 91 otoliths of cod over a period of about 20 years. Seasonal δ¹⁸O_A variations of individual otoliths started at an initial value of about ?0.5 to 0‰ VPDB, and then reached a stable level in the range of +2.5 to +3.5‰ VPDB after 4–5 years. The initial low values correspond to the natal sources of mature cod, while the higher δ¹⁸O_A values represent the water conditions before the cod was caught. This pattern of δ¹⁸O_A variation was observed over the life history of all cod examined. Furthermore, the calculated isotopic temperatures agreed with those obtained from summer bottom trawl survey, indicating that δ¹⁸O_A of otoliths could be used as a thermometer in determining the ambient seawater temperature where the cod lived. Comparison of long-term δ¹⁸O_A records and biological and meteorological observations suggested that decadal-scale ecosystem changes did occur in the late 1970s and early 1990s in Atlantic Canada, comparable to regime shifts occurred in the North Pacific.     

Isotopic characteristics of meteoric waters in the Belgrade region

Abstract

The stable isotope composition of hydrogen (δ²H) and oxygen (δ¹⁸O) in monthly precipitation and river water (Sava River and Danube) samples in the Belgrade area gathered between 1992 and 2005 are determined. The local meteoric water line δ²H=7.8 (±0.2) δ¹⁸O+7.3(±1.6) (r ²=0.98, n=60, σ=0.52) for the whole period of observation is close to the global meteoric water line. The amount-weighted mean δ²H and δ¹⁸O values of precipitation were?65±27 ‰ and?9.4±3.4 ‰, respectively. Good correlation between δ¹⁸O values (r>rsim0.67) and ambient temperature and relative humidity was obtained. Stream-water data ranged from?94 to?60 ‰ for δ²H and from?11.0 to ～5.7 ‰ for δ¹⁸O with highly statistically significant difference (p>0.01) between the Sava River and the Danube. In addition, the isotopic compositions of local precipitation and adjacent river water at monitoring sites were compared. Obtained data will give an opportunity to improve the knowledge of mixing stream water and local groundwater, and assessment of potential groundwater risks and pressures in the Belgrade basin.     

Oxygen and nitrogen isotopic composition of nitrate in commercial fertilizers,nitric acid,and reagent salts

Nitrate is a key component of synthetic fertilizers that can be beneficial to crop production in agro-ecosystems, but can also cause damage to natural ecosystems if it is exported in large amounts. Stable isotopes, both oxygen and nitrogen, have been used to trace the sources and fate of nitrate in various ecosystems. However, the oxygen isotope composition of synthetic and organic nitrates is poorly constrained. Here, we present a study on the N and O isotope composition of nitrate-based fertilizers. The δ¹⁵N values of synthetic and natural nitrates were 0?±?2?‰ similar to the air N₂ from which they are derived. The δ¹⁸O values of synthetic nitrates were 23?±?3?‰, similar to air O₂, and natural nitrate fertilizer δ¹⁸O values (55?±?5?‰) were similar to those observed in atmospheric nitrate. The Δ¹⁷O values of synthetic fertilizer nitrate were approximately zero following a mass-dependent isotope relationship, while natural nitrate fertilizers had Δ¹⁷O values of 18?±?2?‰ similar to nitrate produced photochemically in the atmosphere. These narrow ranges of values can be used to assess the amount of nitrate arising from fertilizers in mixed systems where more than one nitrate source exists (soil, rivers, and lakes) using simple isotope mixing models.     

Natural and anthropogenic variations in the Po river waters (northern Italy): insights from a multi-isotope approach

Po is the main Italian river and the δ¹⁸O and δ²H of its water reveal a similarity between the current meteoric fingerprint and that of the past represented by groundwater. As concerns the hydrochemisty, the Ca–HCO₃ facies remained constant over the last 50 year, and only nitrate significantly increased from less than 1?mg/L to more than 10?mg/L in the 1980s, and then attenuated to a value of 9?mg/L. Coherently, δ¹³C_DIC and δ³⁴S_SO4 are compatible with the weathering of the lithologies outcropping in the basin, while extremely variable δ¹⁵N_NO3 indicates contribution from pollutants released by urban, agricultural and zootechnical activities. This suggests that although the origin of the main constituents of the Po river water is geogenic, anthropogenic contributions are locally significant. Noteworthy, the associated aquifers have the same nitrogen isotopic signature of the Po river, but are characterized by significantly higher NO^– ₃ concentration. This implies that aquifers’ pollution is not ascribed to inflow of current river water, and that the attenuation of the nitrogen load recorded in the river is not occurring in the aquifers, due to their longer water residence time and delayed recovery from anthropogenic contamination.     

Deuterium and Oxygen-18 in Surface Waters of GDR draining to the Baltic Sea

A general view is presented of deuterium and ¹⁸O measurements of water samples collected at running and standing surface waters in German Democratic Republic. The values confirm earlier observations that the surface waters are influenced by evaporation with respect to the isotopic composition of groundwater. Nevertheless, stronger evaporation effects are restricted to larger lakes. The amount of surface water discharge from GDR to the Baltic Sea and the δD and δ¹⁸O values are discussed. The river Oder provides about 90% of the whole surface run-off. The other watercourses to the coast are unimportand. The mean heavy isotope content of surface run-off was calculated to be ?8.3‰ for δ¹⁸O and ?61‰ for δD (vs. SMOW), respectively.     

Comparison of sample preparation methods for stable isotope analysis of dissolved sulphate in forested watersheds

Pretreatment methods for measuring stable sulphur (δ³⁴S) and oxygen (δ¹⁸O) isotope ratios of dissolved sulphate from watersheds have evolved throughout the last few decades. The current study evaluated if there are differences in the measured stable S and O isotope values of dissolved sulphate from forested watersheds when pretreated using three different methods: Method 1 (M1): adsorb sulphate on anion exchange resins and send directly to isotope facility; Method 2 (M2): adsorb sulphate on anion exchange resins, extract sulphate from anion exchange resins, and send the produced BaSO₄ to the isotope facility; and Method 3 (M3): directly precipitate BaSO₄ without anion exchange resins with the precipitates being sent to the isotope facility. We found an excellent agreement of the δ³⁴S_sulphate values among all the three methods. However, some differences were observed in the δ¹⁸O_sulphate values (M1 versus M2:?1.5 ‰; M1 versus M3:?1.2 ‰) associated with possible O contamination before isotope measurement. Several approaches are recommended to improve the pretreatment procedures for δ¹⁸O_sulphate analysis.     

Spatial and temporal variability of stable isotopes and biological parameters for the Danube River in Serbia

This paper presents the results of hydrological, physicochemical, biological, and isotopic investigations of the Danube River along the stretch through Serbian territory conducted during four campaigns in September and November 2007, September 2008 and April 2009. The stable isotope values exhibited significant changes both in the Danube (?10.7 to?9.5‰ for δ¹⁸O and?73.7 to?67.1 ‰ for δ²H) and in its tributaries (?9.1 to?8.5‰ for δ¹⁸O and?69.4 to?59.4‰ for δ²H) depending on the time of survey, which could be partly attributed to the influences of seasonal effects. Results emphasise the dominant role of tributaries inflows from aquifers along the Danube. The very narrow range of δ¹³C_POC (from?28.9 to?27.4 ‰) was associated with relatively high C/N ratios (C/N>9), and together with δ¹⁵N_TPN values, the date suggested that, in early spring, a major fraction of particulate organic matter was derived from allochthonous matter. An orthogonal varimax rotation of the principal components analysis identified four latent factors (‘mineral related’, ‘biological’, ‘hardness’, and ‘soil inlets’) which are responsible for the data structure covering 79% of the observed variations among the variables studied. A reliable grouping of samples with respect to the season was found.     

Hydrogeochemical and isotopic characterisation of groundwater in a sand-dune phreatic aquifer on the northeastern coast of the province of Buenos Aires,Argentina

This contribution presents the hydrochemical and isotopic characterisation of the phreatic aquifer located in the Partido de la Costa, province of Buenos Aires, Argentina. In the sand-dune barrier geomorphological environment, groundwater is mainly a low-salinity Ca-HCO₃ and Na-HCO₃-type, being in general suitable for drinking, whereas in the continental plain (silty clay sediments), groundwater is a Na-Cl type with high salinity and unsuitable for human consumption. The general isotopic composition of the area ranges from?6.8 to?4.3 ‰ for δ¹⁸O and from?39 to?21 ‰ for δ²H, showing that rainwater rapidly infiltrates into the sandy substrate and reaches the water table almost without significant modification in its isotopic composition. These analyses, combined with other chemical parameters, made it possible to corroborate that in the eastern area of the phreatic aquifer, there is no contamination from marine salt water.     

Two-step synthesis of ethylene glycol-D6 via isotope exchange of glycolic acid

Tracers can be used to monitor emissions of leachate from landfills in order to detect hydrological pathways and to evaluate environmental pollution. We investigated the stable carbon isotope ratio (δ¹³C–Σ CO ₂) in dissolved inorganic carbon and tritium (³H) in water, in addition to the tracers of pollution commonly found in relatively high concentrations in leachate, such as chloride (Cl), organic matter (COD), nitrogen (total and NH₄–N), iron (Fe), electrical conductivity (EC) and pH. The sampling was performed at seven landfills in the south-eastern part of Norway during a period of 5 years. The objective was to evaluate the potential for tracing leachate in the environment with emphasis on groundwater pollution. By measuring the δ¹³C–Σ CO ₂ in leachates, groundwaters and surface waters, the influence of leachate can be identified. The value of δ¹³C–Σ CO ₂ varied from?5.5 to 25.9 ‰ in leachate, from?25.4 to 14.7 ‰ in groundwater and from?19.7 to?13.1 ‰ in creeks. A comparison of the carbon isotope ratio with COD, EC and the concentrations of total and NH ₄–N, Cl and Fe showed that δ¹³C–Σ CO ₂ is a good tracer for leachate due to higher sensitivity compared to other parameters. The mean concentrations of all the studied parameters were higher in the leachate samples; however, only the carbon isotope ratio showed significant differences between all the groups with strong and middle pollution and samples with low pollution, showing that it can be used as a convenient tracer for leachate in groundwater and surface water. The carbon isotope ratio showed strong correlation between nitrogen, EC and bicarbonate, but not with pH. Tritium was only sporadically found in measureable concentrations and is not considered as a suitable tracer at the sampled locations.     

Spring response to precipitation events using δ18O and δ2H in the Tanour catchment,NW Jordan

The Tanour spring is one of the several karst springs located in the northern part of Jordan. Water samples from the Tanour spring and precipitation were collected in the area of Ajloun in NW Jordan for the analysis of stable oxygen and hydrogen isotopes to evaluate the spring response to precipitation events. Rainwater and snow samples were collected from different elevations during winters of 2013–2014 and 2014–2015. In addition, spring samples were collected between December 2014 and March 2015. δ¹⁸O values in rainwater vary from ?3.26 to ?17.34?‰ (average: ?7.84?±?3.23?‰), while δ²H values range between ?4.4 and ?110.4?‰ (average: ?35.7?±?25.0?‰). Deuterium excess ranges from 17.8 to 34.1?‰ (average: 27.1?±?4.0?‰). The Local Meteoric Water Line for the study area was calculated to be δ²H?=?7.66*δ¹⁸O?+?24.43 (R²?=?0.98). Pre-event spring discharge showed variation in δ¹⁸O (range ?6.29 to ?7.17?‰; average ?6.58?±?0.19?‰) and δ²H values (range ?28.8 to ?32.7?‰; average: ?30.5?±?1.0?‰). In contrast, δ¹⁸O and δ²H rapidly changed to more negative values during rainfall and snowmelt events and persisted for several days before returning to background values. Spring water temperature, spring discharge, and turbidity followed the trend in isotopic composition during and after the precipitation events. The rapid change in the isotopic composition, spring discharge, water temperature, and turbidity in response to recharge events is related to fast water travel times and low storage capacity in the conduit system of the karst aquifer. Based on the changes in the isotopic composition of spring water after the precipitation events, the water travel time in the aquifer is in the order of 5–11 days.     

Reliability of stable carbon and oxygen isotope compositions of pedogenic needle fibre calcite as environmental indicators: examples from Western Europe

Stable carbon and oxygen isotope analyses were conducted on pedogenic needle fibre calcite (NFC) from seven sites in areas with roughly similar temperate climates in Western Europe, including the Swiss Jura Mountains, eastern and southern France, northern Wales, and north-eastern Spain. The δ¹³C values (?12.5 to?6.8 ‰ Vienna Pee Dee Belemnite (VPDB)) record the predominant C₃ vegetation cover at the sites. A good correlation was found between mean monthly climatic parameters (air temperature, number of frost days, humidity, and precipitation) and δ¹⁸O values (?7.8 to?3.4‰ VPDB) of all the NFC. Similar seasonal variations of δ¹⁸O values for monthly NFC samples from the Swiss sites and those of mean monthly δ¹⁸O values of local precipitation and meteorological data point out precipitation and preferential growth/or recrystallisation of the pedogenic needle calcite during dry seasons. These covariations indicate the potential of stable isotope compositions of preserved NFC in fossil soil horizons as a promising tool for palaeoenvironmental reconstructions.     

C and O stable isotopic signatures of fast-growing dripstones on alkaline substrates: reflection of growth mechanism,carbonate sources and environmental conditions

Secondary carbonate precipitates (dripstones) formed on concrete surfaces in four different environments – Mediterranean and continental open-space and indoor environments (inside a building and in a karstic cave) – were studied. The fabric of dripstones depends upon water supply, pH of mother solution and carbonate-resulting precipitation rate. Very low δ¹³C (average?28.2‰) and δ¹⁸O (average?18.4‰) values showed a strong positive correlation, typical for carbonate precipitated by rapid dissolution of CO₂ in a highly alkaline solution and consequent disequilibrium precipitation of CaCO₃. The main source of carbon is atmospheric or biogenic CO₂ in the poorly ventilated karstic cave, which is reflected in even lower δ¹³C values. Statistical analysis of δ¹³C and δ¹⁸O values of the four groups of samples showed that the governing factor of isotope fractionation is not the temperature, but rather the precipitation rate.     

Untersuchungen zur Isotopensignatur von Methan und Kohlendioxid aus biogenen Gasen unterschiedlicher Quellen

Abstract

The isotopic compositions of biogenic carbon dioxide and methane from different sites were investigated. The δ¹³C values of methane vary mainly between ?55‰ and ?75‰ whereas δ¹³C values of carbon dioxide were found from about + 11‰ to ?23‰. Especially the latter ones are not so typical for microbial gases. The different sites don't vary over the whole scales but form certain groups. Secondary effects like diffusion change the δ values of both components in an even more negative direction, while oxidation processes near the surface result in more positive δ¹³C values for methane and very negative δ¹³C values for carbon dioxide.     

Stable isotope mass balances versus concentration differences of dissolved inorganic carbon – implications for tracing carbon turnover in reservoirs

The aim of this study was to identify sources of carbon turnover using stable isotope mass balances. For this purpose, two pre-reservoirs in the Harz Mountains (Germany) were investigated for their dissolved and particulate carbon contents (dissolved inorganic carbon (DIC), dissolved organic carbon, particulate organic carbon) together with their stable carbon isotope ratios. DIC concentration depth profiles from March 2012 had an average of 0.33 mmol L^–1. Increases in DIC concentrations later on in the year often corresponded with decreases in its carbon isotope composition (δ¹³C_DIC) with the most negative value of –18.4?‰ in September. This led to a carbon isotope mass balance with carbon isotope inputs of ?28.5?‰ from DOC and ?23.4, ?31.8 and ?30.7?‰ from algae, terrestrial and sedimentary matter, respectively. Best matches between calculated and measured DIC gains were achieved when using the isotope composition of algae. This shows that this type of organic material is most likely responsible for carbon additions to the DIC pool when its concentrations and δ¹³C_DIC values correlate negatively. The presented isotope mass balance is transferable to other surface water and groundwater systems for quantification of organic matter turnover.